1. Field of Invention
The invention relates generally to a loudspeaker of the type having a magnetic circuit comprising a permanent magnet upon which is positioned a top plate or “core cap.” In particular, the invention relates to an improved core cap that increases its capacity to use the magnetic energy available from the magnet, while maintaining advantageous features for simplifying loudspeaker assembly.
2. Related Art
Loudspeakers may have a shell-pot design. Such loudspeakers are commonly of physically small dimensions and are used in loudspeaker applications for reproducing sound in the mid-to-high frequency ranges, such as a tweeter, for example. In FIG. 1, a simplified cross-section of a typical loudspeaker 100 of this type is shown.
The loudspeaker 100 is a diaphragm-type loudspeaker. Loudspeaker 100 includes a magnetic circuit 102 that produces a stationary magnetic field of high flux density in a narrow, working air gap 104 where a movable, current-carrying voice coil 106 is located. A force induced by the interaction between the current carried in the voice coil 106 and the magnetic flux in the air gap 104 actuates an assembly 108 for producing sound. The sound producing assembly 108 comprises the voice coil 106, a diaphragm or cone 112, and a suspension or surround 116. The diaphragm 112 moves in response to the force and displaces air to produce a sound.
A shell-pot 118 comprises a lipped, radial basin inside which is located a generally cylindrical permanent magnet 120. A disk-like core cap 122 is attached to the top of the magnet 120. Typically, the core cap 122 has a slightly greater diameter than the permanent magnet 120 so that it may extend beyond the periphery of the magnet, and is adhered to the magnet 120 by an adhesive. The working air gap 104 surrounds core cap 122 and spans the distance between the core cap 122 and the adjacent inside surface of the shell-pot 118.
The magnetic circuit 102 is formed as the magnet 120 generates a magnetic field and the core cap 122 and shell-pot 118 each provide a path from the opposite poles of the permanent magnet 120 for carrying and directing the magnetic field into the air gap 104.
A cross-section of a typical core cap 122 is shown in FIG. 2. As is illustrated, a small circular groove 202 has a diameter that is slightly less than the diameter of the core cap 122, so that the groove 202 is near to the perimeter of the core cap 122. The groove 202 is formed in the surface or face 201 of the core cap 122 that is to be adhered to the permanent magnet 120. The purpose of the groove 202, which is commonly referred to as an adhesive control groove, is to act as a reservoir for collecting any excess adhesive and prevent the adhesive from “squeezing out” from between the magnet 120 and core cap 122 and into the air gap 104 during assembly.
The opposite face 203 of the core cap 122 also includes a second and identical adhesive control groove 200. The additional groove 200 eliminates any need to particularly orient the core cap 122 prior to its assembly to the permanent magnet 120 and, thus, makes the assembly process error-proof in this regard. Though convenient for manufacturing, the additional groove 200 may create unintended problems in the operation of the core cap. It is therefore desirable to provide a core cap that not only possesses the features advantageous for the manufacturability of the loudspeaker (e.g., take an adhesive reservoir and assembly orientation error-proofing) but also reduces unintended problems in the operation of the core cap.